Solid freeform fabrication (SFF) is a collection of processes, such as three-dimensional printing and stereolithography, for manufacturing three-dimensional objects by sequentially depositing layers of a building material. In three-dimensional printing, the object is formed by selectively depositing material from an inkjet print head based on cross sections of the object. Typically, the ink jet print head is supported on a movable print carriage that moves linearly in a main scanning direction (X direction) over a fabrication surface and traverses in a secondary indexing direction (Y direction) for repositioning the print head prior to commencing a new scan in the X direction. The print head is controlled to eject drops of material at appropriate locations pursuant to command of a controller, where the locations correspond to a pattern of pixels corresponding to a cross section of the object. The scanning operation may require high positional precision which is usually achieved by using a high-quality linear encoder to generate trigger pulses for printing. Repositioning the print head along the indexing direction may also require high positional precision. Often, in order to reduce cost, indexing motions are not controlled by an encoder. In these cases, when the motion drive system includes rubber belt system or any other resilient elements, hysteresis errors in the motion, which are unpredictable and therefore cannot be easily corrected, often accrue.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the drawings have not necessarily been drawn accurately or to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity or several physical components included in one functional block or element. Further, where considered appropriate, reference numerals may be repeated among the drawings to indicate corresponding or analogous elements. Moreover, some of the blocks depicted in the drawings may be combined into a single function.